This invention relates to television special effects, and more particularly to a method and apparatus for producing a border having selected characteristics around a selected object on a video image.
It is frequently desirable in dealing with visual images to obtain an image having particular characteristics. If an appropriate scene is available, then an image may be directly captured on appropriate media, such as film or video tape, for subsequent use. However, it is often the case that a desired image is not directly available, and must consequently be created. In such a case, the desired image may be indirectly produced through the use of special techniques, broadly referred to as special effects. In such a process, a desired visual image may be artificially created through the combination of visual information from various sources. The manner in which the visual information from the various sources is combined is determined by the desired effect, there being many ways and techniques in which visual information may be combined. Consequently, desired visual images which are themselves not directly available may often be indirectly produced through the use of a variety of special effects. Such techniques operate to extend the horizon of visual images available for use in various applications. Such techniques typically find great demand in the fields of entertainment and commercial product or service advertisement. There is consequently a large interest in the field of special effects.
A special effect of particular interest is that of producing a glow around a selected object. Broadly speaking, a glow is a fringe of light surrounding an object, the intensity of which decreases with distance from the object. A further property of glow is that the background image over which the glow is superimposed may be seen through the glow. In the past, this has been accomplished in a number of different ways.
One method employed to produce a glow around an object involves the use of animation techniques. In particular, the object around which a glow is desired is first photographed on an appropriate media. Thereafter, positional information with respect to the location and shape of the desired glow is determined. Next, appropriate art work is prepared according to the desired glow. In particular, the general shape, width, amount of glow, color and other associated parameters are determined and used to construct the appropriate art work. Thereafter, the art work is photographed. The resulting photograph is then combined with the original visual information in a mixing process appropriate for the media in use. The resulting visual image will consequently be the original image with the desired glow there around.
While the use of animation techniques does provide for a wide variety of special effects, it is apparent that the process necessarily involved in the production of the desired glow is somewhat labor intensive and time consuming. In addition, the nature of the process does not provide for ease in varying of the parameters associated with the glow. To the contrary, the changing of a parameter would generally require the repetition of the complete process. Consequently such a process necessarily is not only somewhat tedious and expensive, but also inflexible.
An alternate approach to the process of producing a glow around a selected object involves the use of a defocused image. Broadly stated, two images of the object around which the glow is desired are used. One of the images, however, is created by defocusing the associated camera by a selected amount. The image produced by the defocused camera is consequently not sharp, but blurred in accordance with the amount of defocusing employed. The image from the properly focused camera is then superimposed over the image from the defocused camera; the image from the defocused camera thereby producing the appearance of a glow around the selected object. Implementation of the foregoing described defocused image technique could be achieved in the film media in various ways. One such way would employ two separate cameras to obtain the two images. However, such an approach presents a problem of correct registration of the resulting images, as different perspectives result from the differing positions of the two cameras. A second approach employing the use of film media employs a single camera, and a subsequent double exposure process. However, such a technique necessarily involves a certain amount of trial and error. An alternate approach employing video media includes the technique of using a single video camera. A first image is obtained of the desired object with the video camera defocused by a selected amount. The defocused image is thereafter stored. The mechanism employed to store the defocused image could be any of a wide variety of storage devices, including a video tape recorder, or devices capable of storing a frame of video information, commonly referred to a frame store. A second video image of the desired image, correctly focused, is thereafter obtained. The two video images are then mixed in a video mixer. Associated parameters such color characteristics of the glow could be obtained by a wide variety of techniques, including the use of optical filters on the defocused camera, or the electronic generation of the desired color.
However, notwithstanding the choice of media, several shortcomings are apparent. First, the amount of control over the glow is dependent upon the optical characteristics of the lense employed. Consequently control over such parameters as width and intensity of the glow are somewhat indirect. In addition, a somewhat tedious alignment process may also be necessary to ensure proper registration of the focused image over the defocused image. Furthermore, the color desired for a glow is not necessarily easily changeable, depending upon the media in which the glow effect is produced. In further addition to the foregoing, and of perhaps more significance is the fact that none of the foregoing methods of producing a glow around a selected object provide for the production thereof in a real time environment. In particular, with each of the foregoing, it is necessary to perform varying amounts of work to achieve a glow around a selected object. If the object should thereafter be displaced in position, the glow would not follow the displacement of the object. Consequently, it is not possible to create a glow in a real time environment in such a manner that the glow would follow displacement of the object around which the glow is created.
It is consequently apparent from the foregoing that the production of a glow around a desired object is a somewhat indirect process having significant shortcomings.